U.S. patent application number 14/068301 was filed with the patent office on 2014-05-01 for plasma treatment of film for impurity removal.
The applicant listed for this patent is Applied Materials, Inc.. Invention is credited to Joshua COLLINS, Avgerinos V. GELATOS, Michael JACKSON, Amit KHANDELWAL, Benjamin C. WANG.
Application Number | 20140120700 14/068301 |
Document ID | / |
Family ID | 50547627 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140120700 |
Kind Code |
A1 |
WANG; Benjamin C. ; et
al. |
May 1, 2014 |
PLASMA TREATMENT OF FILM FOR IMPURITY REMOVAL
Abstract
Methods for plasma treatment of films to remove impurities are
disclosed herein. Methods for removing impurities can include
positioning a substrate with a barrier layer in a processing
chamber, the barrier layer comprising a barrier metal and one or
more impurities, maintaining the substrate at a bias, creating a
plasma comprising a treatment gas, the treatment gas comprising an
inert gas, delivering the treatment gas to the substrate to reduce
the ratio of one or more impurities in the barrier layer, and
reacting a deposition gas comprising a metal halide and
hydrogen-containing gas to deposit a bulk metal layer on the
barrier layer. The methods can further include the use of diborane
to create selective nucleation in features over surface regions of
the substrate.
Inventors: |
WANG; Benjamin C.; (Santa
Clara, CA) ; COLLINS; Joshua; (Sunnyvale, CA)
; JACKSON; Michael; (Sunnyvale, CA) ; GELATOS;
Avgerinos V.; (Redwood City, CA) ; KHANDELWAL;
Amit; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
50547627 |
Appl. No.: |
14/068301 |
Filed: |
October 31, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61720901 |
Oct 31, 2012 |
|
|
|
Current U.S.
Class: |
438/477 |
Current CPC
Class: |
C23C 16/0227 20130101;
H01L 21/76877 20130101; H01L 21/28556 20130101; H01L 21/76843
20130101; C23C 16/14 20130101; H01L 21/76862 20130101; H01L
21/76876 20130101 |
Class at
Publication: |
438/477 |
International
Class: |
H01L 21/768 20060101
H01L021/768 |
Claims
1. A method for removing impurities, comprising: positioning a
substrate with a barrier layer in a processing chamber, the barrier
layer comprising a barrier metal and one or more impurities;
maintaining the substrate at a bias; creating a plasma comprising a
treatment gas, the treatment gas comprising an inert gas;
delivering the treatment gas to the barrier layer to reduce the
ratio of one or more impurities in the barrier layer; and reacting
a deposition gas comprising a metal halide and hydrogen-containing
gas to deposit a bulk metal layer on the barrier layer.
2. The method of claim 1, wherein the barrier metal is either
tungsten or titanium.
3. The method of claim 1, wherein the treatment gas comprises a gas
selected from the group consisting of helium (He), neon (Ne), argon
(Ar), krypton (Kr), gaseous hydrogen (H.sub.2) or combinations
thereof.
4. The method of claim 1, further comprising maintaining the
substrate at a first temperature during plasma treatment.
5. The method of claim 4, wherein the first temperature is from
250.degree. C. to 450.degree. C.
6. The method of claim 1, wherein the bias is an RF bias from 2 MHz
to 60 MHz.
7. The method of claim 1, wherein the bias is less than the sputter
threshold of the barrier metal.
8. The method of claim 1, wherein the plasma is created from an RF
source with a frequency from 400 KHz to 60 Mhz.
9. The method of claim 1, wherein the metal halide is selected from
the group consisting of tungsten hexafluoride (WF.sub.6), tungsten
hexachloride (WCl.sub.6) and combinations thereof.
10. The method of claim 1, wherein the metal halide is selected
from the group consisting of titanium tetrafluoride (TiF.sub.4),
titanium tetrachloride (TiCl.sub.4) and combinations thereof.
11. The method of claim 1, wherein the bulk metal layer is
deposited at a temperature between 250.degree. C. and 350.degree.
C.
12. The method of claim 1, wherein the one or more impurities
comprise nitrogen, oxygen, carbon or combinations thereof.
13. A method for removing impurities, comprising: positioning a
substrate in a processing chamber, the substrate comprising: an
upper surface having one or more features; and a barrier layer
formed over the upper surface and the one or more feature, where
the barrier layer comprises tungsten and nitrogen; creating a first
plasma comprising a first treatment gas, the first treatment gas
comprising an inert gas; delivering the first treatment gas to the
barrier layer to reduce the ratio of one or more impurities in the
barrier layer; exposing the barrier layer to diborane
(B.sub.2H.sub.6) gas to deposit a layer of adsorbed boron in the
barrier layer; creating a second plasma comprising a second
treatment gas, the second treatment gas comprising an inert gas;
delivering the second treatment gas to the barrier layer while
maintaining the substrate with a bias at a voltage less than the
sputter threshold of the barrier metal to remove boron from the
upper surface; exposing the barrier layer to a gas mixture
comprising WF.sub.6 to deposit a thin layer of tungsten in the
features; and reacting a deposition gas comprising a tungsten
halide and hydrogen-containing gas to deposit a bulk tungsten layer
on the thin layer of tungsten and the barrier layer.
14. The method of claim 13, wherein the bias voltage is greater
than the threshold required to strip adsorbed B.sub.2H.sub.6 or
boron.
15. The method of claim 13, wherein the treatment gas comprises a
gas selected from the group consisting of He, Ne, Ar, Kr, H.sub.2
or combinations thereof.
16. The method of claim 13, further comprising delivering a
treatment bias while the substrate receives the first plasma.
17. The method of claim 16, wherein the bias is an RF bias from 2
MHz to 60 MHz.
18. The method of claim 13, wherein the plasma is created from an
RF source with a frequency from 400 KHz to 60 Mhz.
19. The method of claim 13, wherein the bulk metal layer is
deposited at a temperature between 250.degree. C. and 350.degree.
C.
20. The method of claim 1, wherein the one or more impurities
comprise nitrogen, oxygen, carbon or combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional Patent
Application Ser. No. 61/720,901 (APPM/17580L), filed Oct. 31, 2012,
which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention relate generally to methods for
processing a substrate during semiconductor manufacturing.
Specifically, embodiments of the invention relate to methods of
treating a nucleation layer prior to a CVD deposition process.
[0004] 2. Description of the Related Art
[0005] Reliably producing nanometer-sized features is one of the
key technologies for the next generation of semiconductor devices.
The shrinking dimensions of circuits and devices have placed
additional demands on processing capabilities. The multilevel
interconnects that lie at the heart of integrated circuit
technology require precise processing of high aspect ratio
features, such as vias and other interconnects. Reliable formation
of these interconnects is very important to future success and to
the continued effort to increase circuit density and quality of
individual substrates.
[0006] Metallization of features formed on substrates includes CVD
deposition of metals such as tungsten. Tungsten can be used for
metal fill of source contacts, drain contacts, metal gate fill and
gate contacts as well as applications in DRAM and flash memory.
Growth of CVD tungsten from WF.sub.6 and H.sub.2 gas mixtures
typically requires a pre-deposited underlayer of metallic tungsten
to crack H.sub.2 into adsorbed atomic hydrogen and to initiate
metal film growth.
[0007] In previous techniques, a tungsten nucleation layer is
deposited from WF.sub.6 and SiH.sub.4 or WF.sub.6 and
B.sub.2H.sub.6 on a barrier and adhesion layer of TiN or WN by an
ALD process. However, this technique is rapidly losing
extendability into less than 20 nm features due to the increasing
volume fraction of the feature being consumed by the barrier metal
and ALD-W nucleation.
[0008] Therefore, there is much effort in the art to create a
tungsten deposition process which reduces the use of intermediate
layers prior to bulk tungsten fill.
SUMMARY OF THE INVENTION
[0009] Embodiments of the present invention generally provide
methods of CVD deposition of metals in small features while
reducing resistance of underlying layers. Specifically, the present
invention generally provides methods to both control deposition of
metals into trenches and vias while reducing the undesired effects
of nucleation layers. In one embodiment, a method for removing
impurities can include positioning a substrate with a barrier layer
in a processing chamber, the barrier layer comprising a barrier
metal and one or more impurities, maintaining the substrate at a
bias, creating a plasma comprising a treatment gas, the treatment
gas comprising an inert gas, delivering the treatment gas to the
barrier layer to reduce the ratio of one or more impurities in the
barrier layer, and reacting a deposition gas comprising a metal
halide and hydrogen-containing gas to deposit a bulk metal layer on
the barrier layer.
[0010] In another embodiments, a method for removing impurities can
include positioning a substrate in a processing chamber, creating a
first plasma comprising a first treatment gas, the first treatment
gas comprising an inert gas, delivering the first treatment gas to
the barrier layer to reduce the ratio of one or more impurities in
the barrier layer, exposing the barrier layer to diborane
(B.sub.2H.sub.6) gas to deposit a layer of adsorbed boron in the
barrier layer, creating a second plasma comprising a second
treatment gas, the second treatment gas comprising an inert gas,
delivering the second treatment gas to the barrier layer while
maintaining the substrate with a bias at a voltage less than the
sputter threshold of the barrier metal to remove boron from the
upper surface, exposing the barrier layer to a gas mixture
comprising WF.sub.6 to deposit a thin layer of tungsten in the
features, and reacting a deposition gas comprising a tungsten
halide and hydrogen-containing gas to deposit a bulk tungsten layer
on the thin layer of tungsten and the barrier layer. In this
embodiment, the substrate can include an upper surface having one
or more features, and a barrier layer formed over the upper surface
and the one or more feature, where the barrier layer comprises
tungsten and nitrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0012] FIG. 1 is a cross-sectional view of a substrate with a
feature according to standard tungsten deposition techniques;
[0013] FIG. 2 is a block diagram of a method for depositing a fill
layer according to one embodiment;
[0014] FIG. 3 is a block diagram of a method for depositing a fill
layer according to one embodiment;
[0015] FIG. 4 is a table depicting the barrier layer film
properties both with and without plasma treatment, according to one
embodiment; and
[0016] FIG. 5 is a graph of tungsten growth on a WN barrier layer
in the presence and absence of plasma treatment.
[0017] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one embodiment may be beneficially utilized on other
embodiments without specific recitation.
DETAILED DESCRIPTION
[0018] Embodiments of the present invention generally provide
methods of CVD deposition of metals, such as tungsten, in small
features while reducing resistance of or removing the need for
underlying layers. Deposition of tungsten in features by standard
techniques can lead to an increase in both the starting bulk and
the overall resistance of the deposition product. Tungsten
nucleation layers and in particular ALD nucleation layers from
B.sub.2H.sub.6 and tungsten hexafluoride (WF.sub.6) have been
successful in terms of conformality and in promoting good tungsten
fill for features less than 32 nm, but are generally highly
resistive compared to tungsten from WF.sub.6 and H.sub.2.
Experimentally determined resistance for ALD tungsten deposited
from B.sub.2H.sub.6 and WF.sub.6 is approximately 150
.mu..OMEGA.-cm in comparison to CVD tungsten deposition from
WF.sub.6 and H.sub.2 which is less than 20 .mu..OMEGA.-cm. Both the
ALD tungsten and the CVD tungsten are subsequently deposited on a
tungsten nitride (WN) layer to increase adhesion to underlying
surfaces. By removing impurities such as oxygen, nitrogen and to a
lesser extent carbon from an upper most layer of the WN, an exposed
tungsten layer is created. The exposed tungsten layer can be used
as a nucleation layer, thus providing a new means for conformal
deposition of tungsten.
[0019] Though exemplary embodiments and explanations focus on
tungsten or titanium, it is understood that metals other than
tungsten can used with the deposition techniques described herein
without diverging from the invention as disclosed. The invention as
disclosed herein is clarified with reference to the figures
discussed below.
[0020] FIG. 1 is a cross-sectional view of a substrate 100 with a
feature according to standard tungsten deposition techniques. As
depicted herein, the substrate 100 has an upper surface 102 and a
feature 104. The substrate 100 can be of a standard composition,
such as crystalline silicon substrate. The feature 104 can be an
etched feature, such as a via or a trench. The feature formed
therein can have varying cross-sectional dimensions. For example,
the substrate can have a feature with a width that varies from 4-8
nm, an overall depth of 110 nm and an aspect ratio of 25:1.
[0021] A barrier layer 105 can be deposited on the upper surface
102 and the feature 104 creating a conformal layer over the
surfaces. The barrier layer 105 comprises a metal nitride, such as
WN or titanium nitride (TiN). It is believed that the barrier layer
105 assists with conformal binding of later deposited metals to the
surface of the substrate 100, such as bulk deposition of tungsten
by a CVD process.
[0022] A thin metal layer 106 may be deposited by chemical reaction
over the barrier layer 105, such as a thin conformal layer of
tungsten deposited by atomic layer deposition (ALD). A fill layer
108 is deposited conformally over the thin metal layer 106. The
fill layer is generally deposited by a CVD process, such as the
deposition of tungsten from WF.sub.6 and H.sub.2. Once metal growth
is established, it accelerates from the point of nucleation to
create a fill layer 108 in the feature 104 and on the upper surface
104. The thin metal layer 106 is deposited to overcome low
deposition on the barrier layer 105.
[0023] Without intending to be bound by theory, the nitrogen in the
barrier layer 105 is believed to both increase binding of the
deposited metal to the substrate and reduce catalytic activity of
the metal, such as the catalytic activity of tungsten for splitting
gaseous hydrogen (H.sub.2) into atomic hydrogen (H). The thin metal
layer 106 is deposited to increase the catalytic activity on the
barrier layer 105. As the resistance for the thin metal layer is
believed to be approximately 150 .mu..OMEGA.-cm and the resistance
of the fill layer 108 is believed to be less than 20
.mu..OMEGA.-cm, it is desirable to reduce or eliminate the thin
metal layer 106 at least inside the feature 104.
[0024] As the layer grows from all surfaces simultaneously and at
the same rate, two problems can occur. First, as areas of the
feature 104 are growing together simultaneously, a seam 118 can
form when the growth from the fill layer 108 meets. This seam 118
creates space for post-processing reactants to damage the
uniformity of the tungsten fill layer 108, such as those used in
conjunction with a CMP, as well as creating voids. Second, the thin
metal layer 106 is expected to affect the resistivity of the
overall fill in a feature 104 with smaller cross-sectional
dimensions. As the thin metal layer 106 occupies more space in
smaller features, such as the feature 104 with cross sectional
dimensions of less than 20 nm, the fill layer 108 does not occupy
as much of the feature 104.
[0025] The method described herein helps avoid both seam formation
and increased resistivity. By treating a portion of the barrier
layer 105 to remove the impurities, such as oxygen, nitrogen and
carbon, a portion of the WN surface can be converted to a
substantially tungsten surface. The bulk of the barrier layer 105
remains WN (surface binding is not affected) while an upper portion
of the barrier layer 105 is converted to tungsten. The presence of
tungsten in the barrier layer 105 allows the barrier layer 105 to
catalyze the formation of the fill layer 108 without a thin metal
layer 106.
[0026] FIG. 2 is a block diagram of a method 200 for depositing a
fill layer according to one embodiment. The method 200 can include
positioning a substrate in a processing chamber, as in 202. The
substrate can be of any composition, such as a crystalline silicon
substrate. The substrate can have a WN or a TiN layer deposited
over the surface. The layer can be a primarily WN or TiN layer with
various impurities therein, such as a WN layer with between 35%-60%
tungsten, 20%-30% nitrogen and the remaining comprising oxygen and
carbon. The substrate can also include one or more features, such
as a via or an interconnect. The processing chamber used with one
or more embodiments can be any CVD processing chamber, such as an
Isani XT pre-clean chamber available from Applied Materials, Inc
located in Santa Clara, Calif. Flow rates and other processing
parameters described below are for a 200 mm substrate. It should be
understood these parameters can be adjusted based on the size of
the substrate processed and the type of chamber used without
diverging form the invention disclosed herein.
[0027] The method 200 can further include maintaining the substrate
at a bias, as in 204. The substrate can be maintained at a bias,
such as a bias of between 2 MHz to 60 MHz, with preferred
embodiments of 13.56 MHz. The bias delivered to the substrate
should be less than the energy required for sputtering the WN or
TiN layer. In some embodiments, the bias is significantly lower
than that required for sputtering. In one embodiment, the bias is
delivered to the substrate at a power of between 50 W and 100 W,
such as 75 W. The use of a bias in this embodiment is optional and
is not necessary for the removal of impurities from the surface of
the barrier layer.
[0028] The method 200 can include creating a plasma comprising a
treatment gas, as in 206. A plasma comprising the treatment gas can
be formed by any known mechanism, such as an inductively formed
plasma or a remote plasma. In one embodiment, the plasma is formed
using an RF power source at a frequency of from 400 KHz to 60 MHz.
In exemplary embodiments, the plasma can be formed at a power level
of 450 W to 550 W, such as 500 W. The treatment gas can be formed
from an inert gas, such as helium (He), neon (Ne), argon (Ar), or
krypton (Kr). The treatment gas can also comprise a secondary gas,
such as gaseous hydrogen (H.sub.2). The H.sub.2 can be incorporated
into any inert gas mixture. The H.sub.2 can be incorporated at a
range of 1%-20%.
[0029] The method 200 can include delivering the treatment gas to
the substrate, as in 208. The treatment gas can be delivered either
as a plasma or as an activated gas, such as a gas delivered from a
remote plasma source. The nitrogen is believed to be loosely bound
to the metal. As the treatment gas is delivered to the substrate,
the nitrogen from exposed portions of the barrier layer is
displaced by the inert gas. The inert gas also does not react with
the tungsten and thus impurities are removed from the layer.
[0030] Without intending to be bound by theory, it is believed that
the energy delivered to the plasma and the bias to the substrate
should be maintained so as to prevent sputtering of the barrier
layer. If plasma is produced at an energy level which can sputter
the layer, the plasma treatment can result in barrier damage and
poor sidewall treatment inside high aspect ratio (AR) features. At
or below the sputter threshold, ion directionality of the plasma is
less and plasma treatment time can be extended for treatment of
sidewall features without damage to the field or corners. Though
lighter gases are not as likely to sputter the barrier layer, there
is a possibility of implantation which should also be avoided.
[0031] The substrate temperature may be increased in some
embodiments to achieve a similar result using a lower bias. For
example, the substrate can be maintained at a temperature between
250.degree. C. and 450.degree. C. during the delivery of plasma.
The temperature range restriction relates to the reduced thermal
budget for semiconductors after transistor gate fabrication. As
such, for substrates which, due to composition or lack of such
structures, have a different thermal budget, the temperature range
may be increased or decreased with relation to the thermal budget
required by features on the substrate.
[0032] The method 200 can include reacting a deposition gas to
deposit a fill layer, as in 210. After the tungsten or titanium
surface has been formed from the WN or TiN surface respectively, a
fill layer is deposited by a CVD process. The CVD process can be
any available CVD process, such as a thermal CVD process. The
reactant gases for the CVD can include a metal halide, such as a
tungsten halide or a titanium halide, and a hydrogen-containing
gas, such as H.sub.2. Examples of metal halides can include
TiF.sub.4, TiCl.sub.4, WF.sub.6 or WCl.sub.6.
[0033] Not wishing to be bound by theory, it is believed that the
metal halides are adsorbed on the exposed surface and reacted with
H to form a metal deposition. For example, the tungsten
hexafluoride (WF.sub.6) or tungsten hexachloride (WCl.sub.6) is
believed to be adsorbed on the exposed surface of the substrate
which reacts to form WF.sub.5 and F. The H.sub.2 is believed to be
catalyzed by the exposed and unbound tungsten to form H atoms from
H.sub.2. The H atoms can then react with the adsorbed F to create
HF which desorbs from the surface leaving behind metallic tungsten
and further adsorption sites. The reaction mechanism of WF.sub.6
can be summarized as follows:
WF.sub.6.fwdarw.WF.sub.5+F
H.sub.2.fwdarw.2H
WF.sub.5+6H+F.fwdarw.6HF+W
[0034] WCl.sub.6, TiF.sub.4, and TiCl.sub.4 are believed to have a
similar reaction mechanism. The reaction mechanism above requires
an available catalyst for the formation of hydrogen atoms from
H.sub.2. In the absence of a catalyst, the available binding sites
for WF.sub.6 is rate limiting. Since WN and TiN are not a good
catalysts for the formation of H atoms from H.sub.2, the conversion
of the metal nitride to the metal speeds up catalytic activity in
the barrier layer.
[0035] The WF.sub.6 is adsorbed on all available surfaces but since
the formation of atomic hydrogen from H.sub.2 is catalyzed
significantly better at tungsten surfaces than WN surfaces,
nucleation is slower at WN surfaces than at tungsten surfaces.
Temperature also affects the formation of atomic hydrogen from
H.sub.2. As such, the growth temperature for the fill layer can be
between 250.degree. C. and 450.degree. C., with preferred
embodiments between 300.degree. C. and 350.degree. C. The fill
layer deposited by this embodiment is expected to be deposited
conformally over the substrate as impurities are expected to be
removed from the barrier layer without differentiating between
directionality of the barrier layer. Stated differently, the fill
layer is expected to deposit on the sidewalls of a feature and the
bottom of a feature with a treated barrier layer at a rate expected
from a substrate with a nucleation layer formed over the barrier
layer.
[0036] Once the fill layer is deposited on the barrier layer to a
desired thickness, the method 200 can be halted, as in 212. In
preferred embodiments, the thickness of the upper surface portion
of the fill layer once deposition is complete is between 1500 .ANG.
to 3500 .ANG.. The substrate can then be removed from the chamber
for further processing.
[0037] FIG. 3 is a block diagram of a method 300 for depositing a
fill layer according to one embodiment. The method 300 can include
positioning a substrate in a processing chamber, as in 302. The
substrate and the processing chamber used in this embodiment may be
the same as the ones described with reference to FIG. 2.
[0038] The method 300 can further include maintaining the substrate
at a bias, as in 304. The bias delivered to the substrate should be
less than the energy required for sputtering the WN or TiN layer.
In some embodiments, the bias is significantly lower than that
required for sputtering. The substrate can be maintained at a bias
using the parameters described with reference to FIG. 2. As stated
previously, biasing the substrate is optional.
[0039] The method 300 can include creating a first plasma
comprising a treatment gas, as in 306. A plasma comprising the
treatment gas can be formed by any known mechanism, such as an
inductively formed plasma or a remote plasma. The treatment gas can
be formed from an inert gas, such as helium (He), neon (Ne), argon
(Ar), or krypton (Kr). The treatment gas can also comprise a
secondary gas, such as H.sub.2. The H.sub.2 can be incorporated
into any inert gas mixture.
[0040] Without intending to be bound by theory, hydrogen is
expected to be most beneficial to removal of impurities in
combination with an inert gas. Remote or direct hydrogen containing
plasma are more effective at reducing nitrogen and carbon content
in WN films. However, atomic hydrogen, as formed in a plasma, has a
short lifetime after surface collisions. As inert gases, by
definition, are non-reactive, surface collisions are not expected
to reduce the effectiveness of the inert gases. Thus, the
combination of hydrogen and an inert gases can provide an enhanced
impurity removal for the barrier layer in both field and feature
regions on a substrate.
[0041] The method 300 can further include delivering the first
treatment gas to the substrate, as in 308. The treatment gas can be
delivered either as a plasma or as an activated gas, such as a gas
delivered from a remote plasma source. The nitrogen is believed to
be loosely bound to the metal. As the treatment gas is delivered to
the substrate, the nitrogen from exposed portions of the barrier
layer is displaced by the inert gas. The inert gas also does not
react with the tungsten and thus impurities are removed from the
layer.
[0042] The method 300 can further include exposing the substrate to
B.sub.2H.sub.6, as in 310. After the barrier layer has been treated
with the first treatment gas, the barrier layer can be exposed to
B.sub.2H.sub.6 to adsorb a layer onto the surface. The
B.sub.2H.sub.6 soak can be delivered at a pressure of from 1 Torr
to 30 Torr. The exposure time for the B.sub.2H.sub.6 soak can be
from about 5 seconds to about 15 seconds. The B.sub.2H.sub.6 can be
delivered with an inert gas, such as He, Ne, Ar, Kr or combinations
thereof. The inert gas can be used to maintain a specific pressure
while decreasing the concentration of the B.sub.2H.sub.6 in the gas
mixture. The concentration of B.sub.2H.sub.6 in the gas mixture,
when an inert gas is used, can be from 3 atomic % to 20 atomic %,
with preferred embodiments employing a concentration between 3
atomic percent and 7 atomic percent. In one embodiment, the
B.sub.2H.sub.6 can be delivered to the substrate at a pressure of
15 Torr over 10 seconds at a flow rate of 400 sccm and a
B.sub.2H.sub.6 concentration of 5 atomic %.
[0043] Without intending to be bound by theory, the B.sub.2H.sub.6
is believed to be preferentially applied after the plasma treatment
to ensure nucleation of the fill layer without formation of high
resistivity compounds. Under the described conditions,
B.sub.2H.sub.6 is very reactive. If the substrate is treated with
B.sub.2H.sub.6 before the plasma treatment, a number of exposed
active molecules will be present on the surface of the substrate,
such as nitrogen and carbon. The reaction of the B.sub.2H.sub.6
with the exposed active molecules can create boron nitrides and
boron carbides. Once reacted, the B.sub.2H.sub.6 will not be
available for subsequent reaction. By removing these reactants with
the plasma treatment prior to treatment with B.sub.2H.sub.6, a
reactive species will be deposited which can further react with the
WF.sub.6.
[0044] The method 300 can further include creating a second plasma
comprising a second treatment gas, as in 312. The second plasma can
be of the same composition as the first plasma. The second plasma
comprising the second treatment gas can be formed by any known
mechanism, such as an inductively formed plasma or a remote plasma.
The second treatment gas can be further tailored to preferentially
target specific areas of the substrate. In one embodiment, the
second treatment gas can be primarily a hydrogen gas. As previously
discussed, a hydrogen gas would be expected to be active more at
the surface than in the features. As it is desirable to remove
adsorbed B.sub.2H.sub.6 from the surface and not from the features,
the selectivity of hydrogen for the exposed surfaces over the
features is expected to be beneficial.
[0045] The method 300 can further include delivering the second
treatment gas to the substrate, as in 314. The second treatment gas
can be in the form of a plasma or an activated gas. The second
treatment gas is delivered to the substrate to remove
B.sub.2H.sub.6 and other boron compounds from surface regions of
the barrier layer without removing B.sub.2H.sub.6 from inside the
features. As the B.sub.2H.sub.6 is only loosely bound to the
surface, the inert gas can remove the adsorbed B.sub.2H.sub.6
without affecting the substrate. In preferred embodiments, the
second plasma treatment is done in the presence of a bias. The bias
voltage should be less than sputter threshold of tungsten but
greater than threshold required to strip B.sub.2H.sub.6 or
boron-containing substances from substrate.
[0046] The method 300 can further include exposing the substrate to
a gas mixture comprising a metal halide, as in 316. In this
embodiment, the substrate can then be exposed to a gas mixture
comprising a tungsten halide, such as WF.sub.6 or WF.sub.6 and
B.sub.2H.sub.6, to preferentially initiate nucleation of tungsten
deposition, such as tungsten deposited by a CVD process using
WF.sub.6 and H.sub.2. In this scheme tungsten growth is accelerated
inside feature where plasma treatment is weakest, as the weakest
plasma treatment correlates with increased presence of
B.sub.2H.sub.6. The adsorbed B.sub.2H.sub.6 will allow tungsten to
be deposited on the barrier layer from reaction with WF.sub.6.
After the post treatment with the gas mixture comprising a tungsten
halide, bulk deposition of tungsten, such as by CVD using WF.sub.6
and H.sub.2 will preferentially form over the thin tungsten
nucleation layer inside the feature.
[0047] Without intending to be bound by theory, it is believed that
since the upper surface of the barrier layer is cleaned of
impurities, the high resistance of the ALD nucleation layer can be
avoided. As previously described, B.sub.2H.sub.6 is very reactive.
Further, some of the byproducts of reaction with the non-plasma
treated surface include boron nitrides and boron carbides. Boron
nitrides and boron carbides have a high resistance compared to that
of tungsten. Thus, it is believed that during a standard ALD
process over a barrier layer, boron nitrides and boron carbides are
formed as well as the tungsten which is formed by reaction with
B.sub.2H.sub.6. By removing these impurities prior to a partial ALD
from WF.sub.6 and B.sub.2H.sub.6, it is believed that the
resistivity increase can be at least partially avoided.
[0048] The method 300 can further include reacting a deposition gas
to deposit a fill layer, as in 318. After the tungsten or titanium
surface has been formed from the WN or TiN surface respectively, a
fill layer is deposited by a CVD process. The CVD process can be
any available CVD process, such as a thermal CVD process. The
reactant gases for the CVD can include a metal halide, such as a
tungsten halide or a titanium halide, and a hydrogen-containing
gas, such as H.sub.2. Examples of metal halides can include
TiF.sub.4, TiCl.sub.4, WF.sub.6 or WCl.sub.6. The parameters for
deposition of the fill layer can be the same as those described
with reference to FIG. 2.
[0049] Once the fill layer is deposited on the second nucleation
layer to a desired thickness, the method 300 can be halted, as in
320. In this embodiment, deposition on the upper surface of the
barrier layer is expected to be slower than deposition on the
feature portion of the barrier layer, due to the partially formed
nucleation layer. In preferred embodiments, the thickness of the
upper surface portion of the fill layer once deposition is complete
is between 1500 .ANG. to 3500 .ANG.. The substrate can then be
removed from the chamber for further processing.
[0050] FIG. 4 is a table depicting the barrier layer film
properties both with and without plasma treatment, according to one
embodiment. The table 400 shows density, resistivity and
composition of an exemplary barrier layer prior to fill layer
deposition. The barrier layer of this embodiment is a WN barrier
layer. The density of the barrier layer as deposited was measured
at approximately 14.3 g/cm.sup.3. The resistivity of the layer at
35 .ANG. thickness was determined to be 1128 .mu..OMEGA.-cm. The
composition of the layer as deposited was 40 atomic % tungsten, 27
atomic % nitrogen, 7 atomic % oxygen, and 27 atomic % carbon.
[0051] The WN barrier was then treated with an argon plasma as
described with reference to FIG. 2. Post plasma treatment, a number
of improvements in layer quality were measured in the resulting
barrier layer. The barrier layer density increased to 17.4 as well
as the resistivity of the layer reduced to 480 .mu..OMEGA.-cm. The
composition of the layer after treatment shifted in favor of
tungsten composition which was determined to be approximately 70
atomic % tungsten, 9 atomic % nitrogen, less than 4 atomic %
oxygen, and 21 atomic % carbon. The improvements seen in the
barrier layer are believed to be related to the increased atomic %
tungsten. Further, these benefits are not believed to extend beyond
the upper most surface of the barrier layer, as both the plasma and
bias energy are maintained below the sputtering threshold.
Therefore, the barrier layer can act both to nucleate the fill
layer deposition and to maintain binding of the fill layer to
underlying layers.
[0052] FIG. 5 is a graph of tungsten growth on a WN barrier layer
in the presence and absence of plasma treatment. The graph 500
shows tungsten deposition on both a treated and untreated WN
barrier layer. The barrier layers were either pretreated with an
argon plasma as described with reference to FIG. 2 or untreated.
The bulk tungsten was then deposited by CVD using WF.sub.6 and
H.sub.2 with a pressure of 300 Torr at 300.degree. C. Measurements
of tungsten growth were taken at 1, 2, 3, 4, 6, 7, 8, 9 and 10
seconds for the untreated barrier layer. Measurements of tungsten
growth were taken at 1, 2, 3, 4, and 5 seconds for the treated
barrier layer, due to the significantly more rapid nucleation
rate.
[0053] The nucleation rate on the treated barrier layer is
significantly higher than the untreated barrier layer. By the 1
second time point shown in the graph 500, tungsten growth had
already begun on the treated barrier layer. The untreated barrier
layer show an insignificant level of growth until about 7 seconds
of treatment, indicating a delay in nucleation. Comparatively, the
untreated barrier layer at 7 seconds and the treated barrier layer
at 1 second have approximately the same growth rate, showing that
the effect of the treatment doesn't extend beyond the nucleation of
the fill layer.
[0054] The 6 second shift in nucleation time is believed to be
related to the increased tungsten at the surface of the barrier
layer.
[0055] For further comparison, a substrate with a TiN barrier layer
and a nucleation layer for CVD growth by traditional means is
transposed onto the WN comparison. Though optimal conditions for
growth of the titanium fill layer on the nucleation layer were
used, the tungsten growth on the treated WN barrier layer has the
same nucleation rate as the titanium growth using a traditional
titanium nucleation layer.
Conclusion
[0056] Embodiments of the present invention generally provide
methods of treating a barrier layer to allow nucleation of tungsten
or other metals on treated surfaces and improve feature fill. As
features decrease in size, such as below 20 nm, proper tungsten
fill in those features becomes more difficult. Movement of tungsten
into feature can be inhibited by the nucleation layer itself. As
well, the nucleation layer is believed to have a higher resistivity
than the fill layer. By removing impurities from the preexisting
barrier layer, bulk CVD deposition of tungsten could be nucleated
from the barrier layer itself, thus allowiong bulk deposition in
the absence of a nucleation layer. Further embodiments can include
deposition with a partial nucleation layer, thus increasing
nucleation on features portions of the barrier layer over the upper
surfaces of the barrier layer.
[0057] While the foregoing is directed to embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *